This invention relates to the transmission of data via optical devices, and the monitoring of those devices using sensors.
There is ongoing pressure to increase the speed at which data is transmitted, which in turn is driving the demand for high bandwidth fiber optics components. In these systems, it is often necessary to monitor the light output of the components. Normally, part of the light is diverted to a monitor photodiode—a process that leads to high insertion loss and complicated packaging.
One particular type of optical component uses infrared vertical cavity surface-emitting lasers (VCSEL). While the following discussion focuses on VCSEL-based optical transmission devices, it is understood that other light producing modules may equally employ the described concepts. In existing VCSEL-based optical transmitter packages, a photo-diode is used to monitor the output power from the VCSEL.
In FIG. 1, system 10 illustrates one such commercial package. Provided is a TO Can 12, a sensor 16, such as a silicon photo-diode, a light source 18, such as a VCSEL having a gallium arsenide (GaAs) substrate, a beam splitter 20 and a focusing lens 22 which directs a focused light beam 24 to a fiber optic cable 26. When laser beam 28 impinges upon partial reflector 20, a monitoring light beam 30, which is a portion of laser beam 28, is reflected back to photo-diode 16 to be used to monitor the output power from the VCSEL 18.
This configuration is not conducive to monitoring of the laser power from the back side of the laser 18, since the laser is opaque. The one manner in which to attempt to monitor from the backside would be to etch away the substrate at specified areas.
The approach set forth in FIG. 1 requires the implementation of complicated packaging techniques to align the laser 18, the photo-diode 16, the splitter 20 and the fiber 26. This results in high packaging costs and a higher percentage than desirable of defective systems. It is estimated that when used for transmitters, 90% of the manufacturing cost is directed to the packaging.
Therefore, it has been deemed desirable to find a manner of integrating elements of the system including the VCSELs and photo-diodes as well as potentially optical elements to reduce the packaging costs.